Sunday, May 29, 2011

Rudders, Prop Shaft and a LittleTesting

The propeller hub from Rick arrived in the mail from Australia on Monday, the day after the Commencement Bay Race. It looked much like I expected, and pretty close to the drawing that the local machine shop came up with after examining my hand-drawn scribble.

Here is a picture of it alongside the bushing Rick also sent. This is the piece that is used to keep the shaft from dropping too deep when the boat is not traveling forward.

Since then I've sealed the control arms of the rudders and wrapped them in 4 oz cloth. It took a lot longer to get the cloth right on the arms as it just didn't want to wrap around and stay flat. I ended up using shrink wrap plastic and a couple of spring clips to reduce the bubbles to a minimum.

Since the screws used to secure the cheeks (pulleys) to the boat need something a bit more substantial than mere 4mm of plywood, I added another layer of plywood covered by some 4 oz cloth. The screws will still penetrate into the hull, but they should be fairly well secured by the extra thickness.

The cheeks are used with a cord to pull down the control arms and deploy the rudders. They are plastic wheels with stainless steel bearings, secured with a fairly lightweight stainless bracket and stainless wood screws.

For the propeller shaft I cleaned the 3/8 inch stainless rod and abraded the 4 or 5 inches near one end with the sanding drum of the Moto-tool. I also tried to clean and abrade the inside of the stainless 5/8 ID tubing that will be the part of the shaft that reaches from the gearbox through the stuffing box to the where the shaft emerges underwater.

I wrapped the rod with 4 oz glass that was about 4 inches wide and then saturated it with resin. In retrospect it might have been better to have saturated the cloth first and then wrapped the rod, as it took a lot of massaging the resin into the dry cloth before the resin made it down to metal. After a while, it seemed to be fairly well saturated, but a bit lumpy.

So, after partially rewinding the cloth back on the rod I began inserting the cloth covered end into the waiting stainless tube. Of course, it only went so far and then the cloth bunched up. From here on I slowly rotated the seamless steel tube over the glass covered rod, applying gentle force to insert the rod into the tube. This seems to have worked quite well, as the further the rod was inserted the more the tube had to get inline with the rod.

After several inches of rod and glass were inserted I then wrapped the outside with more glass and resin.

Finally, I took a long strip of shrink wrap plastic and wrapped it over the outer glass and resin to smooth it out and to help force the resin into the cloth.

After all this was done I noticed that a bunch of resin managed to get over sections of both the tubing and rod where it was not wanted. A quick application of a lacquer thinner saturated paper towel made short work of removing that stuff.

I was curious as to how strong the structural fillet material was, and how strong that material was in combination with the lesser 1/4-20 T-nuts. So, a week or two ago I took some excess fillet material and plastered on the bottom and over the flange of a T-nut on a piece of scrap 4mm plywood.

Now that the material had some time to harden, it was time to put it to the test.

The test fixture was a vise to hold the scrap plywood, a 1/4-20 stainless steel bolt, a metal pot that would hang from the bolt, and an assortment of bronze and steel weights.

I screwed the bolt by hand as far as it would penetrate the T-nut. This left the transition point from threaded to non-threaded about 1 inch from the surface of the plane of the plywood. At the transition point I hung the pot.

Taking the bronze weights one by one I placed them in the pot. More and more weights were added, until the pot was completely full.

Nothing happened.

I added weights to the top of the pot, precariously help in place by still more weights.

Nothing happened.

I removed all the weights and weighed them. The total weight with the pot was 32 pounds.

I put the pot back on the bolt and added the 30 pound steel weight. Bronze weights were added again, until no more could be balanced.

Nothing happened.

Removing all the weights and weighing them revealed a total weight of 62 pounds.

So, torque-wise it appears that a basic joint like this can handle 62 inch-pounds with no apparent failure.

If I have more time I'll try to test it to destruction, or at least with the pot at 2 inches from the plane. This would go to 124 inch-pounds.

Wednesday, May 18, 2011


After cleaning up the aka supports and the rudder support on the hull, it was time to continue fabricating the rudders.

Taking the Moto-tool with its sanding drum at the end of the flexible shaft, I trimmed the leading edge of the two rudders at the joint where the reinforcement piece of plywood joins the wider rudder blade. This is where the rudder will be mounted on the outer fiberglass tube which, in turn, rotates about the smaller fiberglass tube previously glued and glassed to the hull.

Using a left over piece of smaller tubing inserted into the two rudder outer tubes in order to keep the rudders concentric, I then carefully balanced the two rudders at 55 degrees plus and minus, mirroring each other, using blocks of scrap foam and some weights to keep things aligned properly. Using several spoonfuls of fillet foam the rudders were then secured to the larger fiberglass tubes. They were left to set overnight.

The next day the rudder assemblies were separated and the fillet material was trimmed and smoothed. The glass and resin that had been applied to the seat, to the aka supports and the rudder supports was also sanded smooth.

The rudders were then mounted on the support shaft, with temporary supports used to hold them parallel to the deck.

After a bit of experimentation I took some scrap plywood that originally had been intended for the aka support bases and trimmed off the beveled edges. These pieces were then placed on the rudders at the pivot points and held in place at the top end with a support structure made from junk found laying about the shop. The angles for the pieces was chosen so they would just intersect with the side of the hull when the rudders were in the fully deployed position. This would align them with the pulleys that would be installed for the control cords that would be used to pull the rudders down into position.

Since there was not much room on the inside between the outer rudder tube and the limit ring, I taped them off with shrink wrap plastic on the top and duct tape on the bottom to hold the shrink wrap in place.

More fillet putty was mixed and liberally applied to the joint on both sides.

The assembly was left to set overnight.

I also started an experiment. Using a large piece of scrap wood, one of the smaller T-nuts and some of the excess fillet putty, I secured the T-nut to the wood and let that sit overnight as well. Tomorrow (2 days later) I'll see how much force is needed to
1. torque it so that the nut spins in place when a bolt threaded into it is rotated.
2. remove it when a tension force is applied to a bolt threaded into it.

Otherwise, today I went on a shopping trip to Online Metals. No, I didn't digitize myself and jump into the computer like the guy in Tron; rather, I drove over to their bricks and mortar location in Ballard, a neighborhood in northwest Seattle.

Their warehouse is located quite close to the Ship Canal leading from Lake Union to Shilshole Bay on Puget Sound. Anyway, I picked up two contenders for the stiff tubing portion of the propeller shaft that connects to the gearbox and fits through the stuffing box to where the more flexible rod portion of the shaft continues onward.

One tube is 0.625 inches OD by 8 feet, with a 0.035 inch wall. The other is 0.5 inches OD by 8 feet, with a 0.049 inch wall. I think the 0.625 inch tubing will do quite nicely, and perhaps might be a bit thicker than needed.

While I was there I also picked up a 1 foot tube of stainless steel to be cut and worked into a coupling between the gearbox and the prop shaft tube.

On the way back home I stopped at Fisheries Supply and picked up some 3mm polyester cord (rated to over 460 pounds) and a pair of cheeks; i.e., pulleys mounted in a stainless steel cage that will be screwed to the hull. These are to be used to pull the rudders down into position and redirect the tensile force of the rope forward to the cockpit.

Since the hull is only 4mm thick, and the forces will be repetitive and possibly somewhat larger than that thickness of wood can handle, I think I'll thicken the hull where the pulleys are mounted with an additional layer of plywood, say 1 inch by 2 inches or so. That should probably be adequate, along with a pair of 1/2 inch #8 wood screws.

It is starting to look like the boat just might not be finished in time for the race this weekend. That might be just as well, as the following race is in a month and I would then have time to do a decent finishing job on the hull, clear coat it, and put it through some trial runs.

Saturday, May 14, 2011

Supports, Support and Supports

Now that the seat back is attached to the hull, it is time to sand it, remove any large bubbles in the fabric or flaws in the resultant glass covering, and check how things are progressing.

The holes drilled for the gearbox support and the hatch were drilled again as the bolts no longer fit due to the resin used to seal the wood. In doing so, some of the wood surfaced, so I decided to use the next size larger bit and re-drill the wood. This way, after I apply resin again, and drill again with the proper sized bit, the wood should remain coated.

A couple of the corners of the seat back needed to be patched as the cloth didn't stay flat against the wood.

Otherwise, the grab tube and glass around the grab tube was very nice and pretty clean. The construction seemed to be very strong, and I could lift the boat by them. Still, I am concerned that there really isn't that much other than the seat back itself structurally securing the tube in place, so I decided to augment that with some 12 oz cloth wrapped over the grab tube and secured to the sides of the hull.

I took advantage of the 12 oz cloth's ability to bunch up by having it bunch up over the top of the grab tube and then spread flat where it attached to the hull. Wrapping the joint a couple of times with shrink wrap helped to keep the glass tight against the side of the seat back, too.

In addition, on the right side where the cloth securing the seat back to the hull extended onto the hull for only an inch or so, I added some 3.5 oz cloth that extended a couple more inches in both directions beyond the 6 oz cloth.

I decided to try an alternate way of securing the wooden reinforcements for the aka supports to the hull. Originally I was planning to sandwich some 12 oz cloth between the deck and wooden reinforcements to accommodate the thickness of the stainless T-nuts. Now, however, I decided to have a thick layer of structural fillet putty there instead as this would better handle the slightly warped wood and fill in the gaps around the T-nuts.

I marked and drilled (on a drill press) the four 1/2 inch holes in the aka support tube bracket. The holes were positioned somewhat close to the outer sides of the bracket, but leaving room for the fender washers.

After marking the deck with the positions of the reinforcement pieces, and measuring (4 times!) the distance to the stern from both sides of the aka support tube bracket placed on said reinforcement pieces, I marked the positions of the drilled holes from the bracket onto the reinforcements. Half-inch holes were then drilled through the reinforcements.

I double checked that the T-nuts fit through the reinforcement pieces, and when mated with the aka bracket the assembly then fit where the markings on the hull indicated. Success!

I cut a 13 by 15 inch rectangle of 3.5 oz cloth on a 45 degree bias to cover the reinforcements and the deck in that area, extending several inches down the sides. I chose a bias angle to enhance how the cloth laid over the corners of the reinforcements and the irregularities between the two pieces.

The T-nut holes were marked on the cloth and, using a home-made die cutter I cut the holes in the cloth for the T-nuts to fit through.

The die cutter was made from a half inch diameter steel tube I had laying about. I sharpened one end of the tube on the bench grinder. After placing the cloth on a piece of pine I took a hammer and pounded out holes in the positions marked on the cloth.

The die cutter worked pretty well. I just had to make sure the cloth was positioned over a fresh area on the board so the fibers were cut.

The fabric fit over the T-nuts like a glove.

Finally, I cut the remaining outer fiberglass tubing into six 3/16 wide rings and two 2.5 inch wide tubes. The 2.5 inch tubes are to be the outer bearings for the dipping rudders, and the rings are to limit the side to side motion of those tubes.

The remaining two rings are to be used with the aka tubes to limit how far they can be inserted into the aka support bracket. I found this feature to be quite useful for the Cadence aka tubes when hunting for the push pin hole.

Rather than rig up another wooden plate support for the rudder axle assembly I decided to merely use fillet material and 12 oz glass, and secure the smaller diameter fiberglass tube to the top of the deck. Two additional 12 oz pieces were used to secure the tube on either side in the same fashion as the grab tube.

The end result was perhaps not as pretty as something done with some sort of wooden reinforcement, but it was a lot faster to make. Perhaps it could be sheathed in wood later on to make it look nicer. All I know is that the aka bracket took way too long and does not look all that good to me!

When doing all this, I mixed 6 heaping spoonfuls of fillet material. There was a bit left over so I spread it onto some shrink wrap. It sort of looked like a Power Bar. Anyway, it might be useful as spacers for the aka bracket if I need to raise it a little.

Monday, May 09, 2011

Seat Attached

Last week I went to West Marine and picked up a 6 inch hatch, a set of bolts to secure it, some small black plastic brackets, and two sizes (1/8 and 3/16 inch) of stretch cords.

They didn't have a hatch that opened with just a quarter turn, but the one I picked up takes only a single turn to seal. That is good enough for my purposes. I chose a transparent one so that it would be easier to check the contents with the hatch in place.

To secure it I chose some #8 stainless machine bolts and nylok nuts rather than wood screws. Wood screws would have been sharp, potentially painful and not as strong in the long run going through 4mm wood and glass.

I took the last remaining large piece of 6 oz cloth and draped it over the seat back structure, stretching from the top of the seat structure, down the seat back and forward over the seat bottom. There was a little bit of excess cloth to be trimmed, but the fragment was just about the perfect size and shape. A couple of additional pieces were cut to cover other strategic areas on the top, sides and front interior where the foam would reinforce the grab tube.

Sunday, after completing editing of the photos from the Lake Whatcom Classic race, I traced out the hole in the right rear panel of the seat back not far from the top of the seat and slightly closer to the front edge of the panel. This would also allow me to access the interior compartment for filleting and glassing the inside joints, or at least that was the plan.

The next step was to glue the seat back to the deck.

First, I mixed up several heaping spoonfuls of seam fillet. This finished off the first container of reddish goo (the green hardener having been used up previously) and started into the second container of green hardener. Once mixed thoroughly it was applied to the foam pieces that would be in contact with the wood and the grab tube. Once each piece was completed it was pressed into place in the frame.

I flipped the back over and carefully put it in place on the deck.

Fillet material was placed in the seams around the base of the seat back, filling the gaps and filleting the inside bottom seams. The gaps around the grab tube were filled, rounded and smoothed.

The two beveled wood pieces I had cut previously to fillet the outside rear panels at the deck were also put in place with fillet material filling the gaps.

I glassed the 6 oz cloth on the seat, and taped the outside seams on the sides with 6 oz cloth.

I had a plan of soaking with resin 12 oz biaxial cloth first, and then applying it to the foam and grab tube inside the seat back compartment. Well, the cloth was nicely soaked, but when it came to applying it to the grab tube it failed miserably. The resin soaked fabric would not stick to the wood and foam; rather, it stuck to the rubber gloves. I tried again and again, until the cloth was nothing but a crumpled mess and could not be salvaged.


I tried again with a smaller piece of dry 6 oz cloth. That worked much better, and I was able to apply enough resin to wet it out. Another try with some additional cloth worked to cover some of the area, but my last attempt with some heavier cloth failed, unfortunately.

Oh, well. Perhaps I'll try again later this week, or maybe just leave it as is, and apply some heavier cloth on the grab tubes and run it partially down the sides of the hull for strength.

On the topic of the propeller hub: I sent a drawing to a local machine shop that claimed to charge $80 per hour. Well, they quoted a price of $175 each for machining 3 hubs.

Methinks I will pursue other options.

Tuesday, May 03, 2011

Fillets for Hand Grips and Seat Back

Since the grab tube is round and the surfaces to which it attaches are all flat, the strength of the bond would be increased significantly if the bonding area was more than the two tangents or the seat back and deck. Of course, the sides where the tube exits the seat back are also fair game for cloth and resin, but this is fairly small contact area as well.

In addition, given the forces applied to the seat back and the grip tubes it would be good to spread them over a larger area. Hence the need to fillet the tube.

Since I am not planning to use the internal foam bulkhead for the seat back that I made a couple of months ago, and since it was the perfect width for the interior of the seat back, I decided to cut pieces of it to make fillets between the seat back and fore side of the tube and deck, the aft side of the tube and deck, and the upper fore side of the tube and the seat back.

I'm planning to fill the gaps at either side of the seat back with epoxy fillet material so that the blue foam will remain sight unseen. The epoxy fillet will be used to fill the other gaps between the seat back and deck, too, though a couple of short pieces of triangular wood fillet like that around the torque box will be used to fillet the outside bottom edge of the aft side of the seat back.

The grab tube was cut to a length of 21.5 inches. This will leave 5 inches exposed on either side of the seat. The remaining 6 inches or so will be used for both the rudder bearings and for insertion limit rings for the akas.

Anyway, it looks like the boat won't quite be done in time for this weekend's race at Lake Whatcom. The amount of work remaining is more than can be done in my evening hours if I also want to get a good night's rest! The forecast is for rain, which means that the Escapade with its bimini roof and semi-enclosed cockpit would be better for race photography.

It would also be good to have some sea trials before racing to make sure things work as planned, so I'm shooting for the Commencement Bay Race towards the end of the month for its racing debut.

Sunday, May 01, 2011

Seat Back and Hand Grips

Early on in this project I had discussed with Rick the possibility of using the hand grips for controlling the rudders. While it might be possible to do so, my original idea of having a lever arm attached to the grips on the outside of the seat back would not work as my body is actually wider than the seat back.

The alternative of having the lever arm inside the seat might be possible, though it would be difficult to adjust or repair even with a hatch in the seat back.

I decided to opt for what might be the simplest approach: use a light rope to pull the rudder blade forward into the water, and a stretch cord to pull the rudder back to the stowed position. If the stretch cord proved to be impractical in practice, then perhaps a second rope could be added to help put the rudder back in the stowed position.

Since I plan to use this boat as a photo platform during races the ropes would be configured to end on the left side of the seat back just above the hand grip. The right rudder rope would have a second rope configured to end on the right side of the seat back, so when my right hand was free it could also be used to steer - at least to the right.

The next thing to decide was which diameter tubing of fiberglass to use for the hand grip. My original plan was to use some of the same tubing as the akas. It is relatively light, adequately strong and somewhat smaller diameter than the second choice.

Both Rick and Cory brought up the idea of using the hand grip tubing to support the akas. Rick indicated that this is how he did it for one of his boats, but found it brought the stabilizers a bit too far forward. He recommended having them mounted several feet further back, which is why I was working on the removable mounting bracket.

After thinking about it further I decided to use the thicker tubing. This would give me two places where the stabilizers could be mounted. Perhaps I am paranoid, but if the bracket broke there would be an alternative that could be used to allow me to recover and keep on going.

If the forward position worked reasonably well, then the complexity of the hull bracket could also be avoided.

Lastly, just as with the Cadence, with the stabilizers mounted right beside the seat I could attach and remove them while on the water. This proved to be very helpful when launching from a dock.

Final resin coat

The hull-mounted aka bracket turned out 50% fine and 50% garbage. On one side the cloth laid nice and flush against the wood on all sides. On the other side it pulled away to make large bubbles, except on the underside where the cloth was pressed against the plastic covered bench.

I removed most of cloth on the bubble side of the bracket using a Moto-tool equipped with a flexible shaft and a tiny sanding drum. It is simply amazing how effect that tiny drum is in removing cured fiberglass!

I used that drum to remove most of the excess resin and glass from the bracket. It fit quite nicely in the filleted corners to round out the rough edges.

The sanding drum generates a lot of very fine particles that I could detect working their way around the seal between my respirator mask and my face. To solution was to hold the shop vac hose next to the drum to suck up the waste. That worked quite well.

After cleaning up once again I tried to glass the ugly side of the aka bracket, and to apply a thin coat of resin to the stabilizers and the final coat on the main hull.

This time, rather than resin the top and side surfaces at the same time I chose to apply resin only to the top surface so as to reduce the occurrence of drips. This was mostly successful, though I managed to miss a couple here and there.

Yesterday I glassed the rudders and made an attempt to fix the still ugly side of the aka bracket, and apply resin to one side of the main hull and the stabilizers. The rudders turned out OK, though they would have been better if they were stood on end rather than laid flat on the plastic covered bench. The excess resin would have pooled at the tip rather than creating a thick bubbly layer. Attacking it with the orbital sander worked fairly well to remove the excess resin.

Since the resin was still slightly soft it came off the surface in larger particles rather than dust. Not bad - perhaps it would clog the shop vac filter somewhat less.

I sanded the drips on the hull and stabilizer, too.

I decided that I would put a hatch in the seat back. This would server two purposes:
1. It would allow me to access the inside of the seat back to apply fillet material and maybe some glass to help better secure the seat to the hull.
2. The space could be used for storage, such as a Camelback water supply, or items that would be accessed when not under way.

Anyway, the chosen panel needed to be glassed on the inside so as to help replace some of the strength lost by the hole for the hatch.

I used 4 oz cloth on the inside and put the seat to one side to cure.

I rediscovered the reason it is better to sand the resin after it has cured. The uncured resin can stay white when a new layer of resin is applied. This obscures the wood finish. least it wasn't in an area that would be too easily seen!